Millimeter wave integrated circuits have become popular for various applications, such as base station wireless backhauls at 40 GHz, 70 GHz and 80 GHz bands, wireless personal networks at 60 GHz band, vehicle collision avoidance radar system at 75 GHz band, security imaging system at 94 GHz band, etc. Notch filters are commonly used for millimeter wave integrated circuits in order to filter out unwanted frequency components, such as image or harmonic generated by nonlinearity of an active device.
On-chip notch filters can be formed using back end of the line (BEOL) processes. In such processes, the notch filters can be provided as microstrip line or coplanar waveguide structures, which have an electrical length of quarter wavelength at the notch frequency and open circuit at one end, as known as a quarter wavelength open stub. Such structures take significant chip area, even though some size reduction techniques can be used, like meandering the straight transmission line structure into serpentine or spiral like structures, which normally use multiple bends. However, such structures may suffer performance degradation.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.